Effect of surface treatments on the shear bond strength of veneering composite resin to CpTi, Ti6Al4V, and BioHPP framework materials: an in vitro study

Background Durable bonding between veneering composite resin and prosthetic framework materials is essential for the performance of veneered restorations. This study evaluated the effects of different surface-conditioning protocols on the shear bond strength (SBS) of veneering composite resin to commercially pure titanium (CpTi), Ti6Al4V alloy, and Bio High-Performance Polymer (BioHPP). Methods Forty-five specimens of CpTi, Ti6Al4V, and BioHPP ( n = 15/material) were divided into three surface-conditioning subgroups ( n = 5): air abrasion with 110-µm Al₂O₃, 98% sulfuric acid etching, and sequential air abrasion followed by sulfuric acid etching. Following material-specific primer application and composite veneering, specimens were stored in distilled water for 24 h and subjected to 5,000 thermocycles. SBS was measured using a universal testing machine. Representative surface morphology was evaluated using scanning electron microscopy (SEM) and atomic force microscopy (AFM), and failure modes were assessed stereomicroscopically. SBS was analyzed using two-way ANOVA followed by Tukey’s HSD test (α = 0.05). Results Framework material (F = 15.20, p < 0.001, partial η² = 0.458) and surface-conditioning protocol (F = 13.02, p < 0.001, partial η² = 0.420) significantly influenced SBS. A significant material × surface-conditioning interaction was also observed (F = 3.17, p = 0.025, partial η² = 0.261). Ti6Al4V subjected to combined air abrasion and sulfuric acid etching demonstrated the highest mean SBS (10.60 ± 4.09 MPa), whereas sulfuric acid-etched BioHPP exhibited the lowest (1.18 ± 1.00 MPa). Air abrasion and combined treatment produced significantly higher SBS than sulfuric acid etching alone (both p < 0.001), with no significant difference between air abrasion and combined treatment ( p = 0.886). All specimens exhibited adhesive failure. Conclusions Framework material and surface-conditioning protocol significantly influenced SBS, with a material-dependent treatment response. Air abrasion, alone or followed by sulfuric acid etching, produced higher SBS than sulfuric acid etching alone. Because material-specific bonding systems were used, inter-material differences should be interpreted as reflecting the complete bonding protocols rather than the isolated effect of framework material alone. Further long-term laboratory and clinical studies are required before definitive clinical recommendations can be made.